1
$\begingroup$

So in my physics book, it is given that light travels in a straight line and this can be concluded as light casts a sharp shadow when it is obstructed by an object.

Now I don't understand how a shadow being sharp relates to the rectilinear propagation of light. Can somebody please explain this to me?

Also, even if this is true, then aren't shadows hazy too?

| cite | improve this question | | | | |
$\endgroup$
1
$\begingroup$

Your book assumes a point source of light. In reality light sources are extended objects; the sun for example has about a half degree apparent width, so shadows cast in sunlight are fuzzy-edged. A sharper shadow can be cast with something like a single LED on the far side of a large room, but because typical LEDs are a few millimeters wide, the shadow will still be fuzzy in close inspection.

Another thing to account for in real environments is reflection from other nearby objects. If even a point source light reflects off, say, a large wall, the reflected light from the wall will cast a hazy shadow.

| cite | improve this answer | | | | |
$\endgroup$
  • $\begingroup$ Alright, but I still don't get how even a point source making a sharp shadow proves that light travels in straight lines... $\endgroup$ – MartianCactus Mar 15 '17 at 16:55
  • $\begingroup$ Because if the light was bending and curving every which way as it traveled, some of it would fall behind the object and the shadow would not be sharp. $\endgroup$ – Asher Mar 15 '17 at 17:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.